1. Field
Embodiments relate to an apparatus for controlling light emitting devices.
2. Background
In accordance with development of semiconductor technologies, efficiency of light emitting diodes (LEDs) has been greatly enhanced. Thus, LEDs have advantages of being economical and environmentally friendly because lifespan is long and energy consumption is small, as compared to existing lighting devices such as incandescent lamps or fluorescent lamps. By virtue of such advantages, LEDs are highlighted as a substitute light source for a backlight of a flat display device such as a liquid crystal display (LCD) or a signal lamp.
Generally, when LEDs are used as a lighting device, plural LEDs are connected in series or in parallel, and turning-on/off thereof is controlled by a light emitting device control apparatus. Generally, such a light emitting device control apparatus, which controls plural LEDs, rectifies alternating current (AC) voltage into ripple voltage, and controls turning-on/off of the plural LEDs, using the rectified ripple voltage.
FIG. 1 is a waveform diagram of ripple voltage generated through full-wave rectification of AC voltage in a conventional light emitting device control apparatus. In FIG. 1, “V” represents voltage, and “I” represents current.
The conventional light emitting device control apparatus full-wave rectifies AC voltage, to convert the AC voltage into ripple voltage as shown in FIG. 1. Using the ripple voltage, the light emitting device control apparatus controls turning-on/off of light emitting devices such as LEDs. Referring to the waveform of FIG. 1, the LEDs repeat turning-on and turning-off in accordance with characteristics of ripple voltage. That is, current having a predetermined pattern is continuously supplied to turn on the LEDs in a section in which the ripple voltage has a level equal to or higher than a predetermined level, in each period. However, in a section 10 in which the ripple voltage has a level lower than the predetermined level, no current is supplied to turn off the LEDs, in each period.
In the conventional light emitting device control apparatus, however, flicker inevitably occurs in the section 10 because turning-on and turning-off are controlled at intervals of very short time. Although it may be difficult to recognize flicker by human eyes, there may be a problem in that, when the eyes of the user are exposed to flicker for a long time, the user may become sensitive and may easily feel fatigued.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.